A plasma processing is a technique indispensable to the manufacture of semiconductor devices. Recently, a design rule for semiconductor devices constituting an LSI becomes further miniaturized in order to comply with a demand for high-integration and high-speed of LSI, and a semiconductor wafer grows in size. Accordingly, a plasma processing apparatus is required to cope with the miniaturization and the size growth.
In case of a parallel plate plasma processing apparatus or an inductively-coupled plasma processing apparatus which has been widely used, plasma damage may occur in a fine-size device due to a high temperature of electrons of a plasma. Further, since a plasma density is kept high only in a limited region, it is difficult to uniformly plasma-process a large-size semiconductor wafer at a high speed.
Therefore, some attention has been paid to a RLSA (Radial Line Slot Antenna) microwave plasma processing apparatus capable of uniformly generating a plasma in a high density and at a low electron temperature (see, e.g., Japanese Patent Application Publication No. 2000-294550). The RLSA microwave plasma processing apparatus includes, as a surface wave plasma generating antenna, a planar antenna (a radial line slot antenna) provided at an upper portion of a chamber, the planar antenna having a plurality of slots formed in a predetermined pattern. In this type of plasma processing apparatus, a microwave generated from a microwave generator passes through the slots of the planar antenna and is radiated into a vacuum chamber through a dielectric microwave transmitting plate provided below the planar antenna. By a thus-produced microwave electric field, a surface wave plasma is generated in the chamber and, thus, a target object, e.g., a semiconductor wafer, to be processed is processed by the plasma.
As for the planar antenna used as the surface wave plasma generating antenna, there is known a planar antenna in which a plurality of, e.g., four, arc-shaped slots is uniformly arranged in a circumferential direction as described in Japanese Patent Application Publication No. 2009-224493 (JP2009-224493A).
However, in the case of using the planar antenna having a plurality of arc-shaped slots uniformly arranged in a circumferential direction as described in JP2009-224493A, the intensity of the electromagnetic wave is decreased at portions where no openings are formed between the slots and the plasma density is also decreased in proportion to the area of that portions. This results in deterioration of the plasma uniformity in the circumferential direction (angular direction).